In just about every story on renewable energy, there’s a familiar cast of characters: green power developers, utilities, and sundry state and federal regulators. But there’s one key player that often lurks in the background – the grid operator.

In the Golden State, most of the power grid is controlled by the California Independent System Operator. Based in a suburb of Sacramento, Cal ISO, as it’s known, essentially ensures that electricity supply and demand stay in balance to prevent brownouts, blackouts, and other catastrophic failures.

The agency also approves requests for big solar power plants, wind farms, and other renewable energy sources to connect to the grid. You may win approval for your project from the California Energy Commission and the United States Interior Department, but unless Cal ISO gives you the green light to plug into the grid, that big solar farm is nothing but a big white elephant.

The prospect of thousands of megawatts of intermittent sources of electricity like solar and wind jolting the grid — and then blinking off when a cloud passes overhead or the wind dies — poses a huge balancing act for grid operators. That’s especially true in place like California, which has mandated that a third of its electricity be generated from renewable sources by 2020.

So it was significant, if little noticed, when Cal ISO this month announced it would begin to integrate energy storage devices like batteries and flywheels into the grid.

Energy storage is increasingly seen as crucial for greening the grid. Electricity from wind farms, which in California typically generate the most power at night when demand is low, could be stored in giant battery arrays and released during the day when demand and rates rise.

Utility Pacific Gas & Electric, for instance, plans to store energy in the form of compressed air pumped into a cavern. When needed, the air would be released to power an electricity-generating turbine. The utility is also exploring using renewable energy to pump water uphill to a reservoir. When demand spikes, the water would be allowed to flow downhill and run a turbine.

And last year, the California Legislature passed a law requiring regulators to determine if the state’s three big investor-owned utilities should be required to generate a certain percentage of electricity from energy storage.

Cal ISO’s early energy storage plans are modest, with just an initial 5 to 10 megawatts of storage integrated into the grid once federal officials given their okay. But it’s likely to be only the start.

“The integration of renewable sources introduces new requirements to reliably manage the grid,” Cal ISO’s chief executive, Yakout Mansour, said in a statement. “Our five-year strategic plan points out that storage technologies bring unique operational solutions to grid management as a tool for helping balance renewables on the system.”

In Wednesday’s New York Times, I wrote about two experimental projects in California to store solar energy produced by photovoltaic rooftop arrays:

In the garage of Peter Rive’s San Francisco home is a battery pack. It is not connected to Mr. Rive’s electric Tesla Roadster sports car, but to the power grid.

The California Public Utilities Commission has awarded $1.8 million to Mr. Rive’s company, SolarCity, a residential photovoltaic panel installer, to research the feasibility of storing electricity generated by rooftop solar arrays in batteries.

As rooftop solar systems provide a growing percentage of electricity to California’s grid, regulators and utilities are increasingly concerned about how to balance the intermittent nature of that power with demand.

One possible solution is to store energy generated by solar arrays in batteries and other systems and then feed that electricity to the grid when, say, a cloudy day results in a drop in power production. And when demand peaks, electricity generated from renewable sources could be dispatched from batteries rather than fossil-fuel burning power plants.

“As soon as distributed solar starts providing 5 to 10 percent of demand, its intermittent nature will need to be addressed,” said Mr. Rive, who is SolarCity’s co-founder and chief operating officer.

SolarCity is teaming with Tesla Motors, the Silicon Valley electric car company run by Mr. Rive’s cousin, Elon Musk, and the University of California, Berkeley, to study how to integrate solar arrays and off-the-shelf Tesla lithium-ion battery backs into the grid. SolarCity plans to put such systems in six homes.

“We think in the years ahead this will be the default way that solar is installed,” Mr. Rive said. “Getting the costs down, though, is not going to be an easy task.”

Homeowners could potentially benefit by tapping batteries at hours when electricity rates are high or using them to provide backup power if the grid goes down.

The research has just begun, and at the moment SolarCity is testing the impact of charging and discharging electricity from the Tesla battery pack in Mr. Rive’s garage. His roof sports a three-kilowatt solar array.

“We’re at the point now where we can direct the battery to charge and discharge at specific times by sending a signal over the Internet,” Mr. Rive said.

Included in the $14.6 million awarded for solar energy storage research by the utilities commission was $1.9 million to SunPower for a project that will store in ice and batteries electricity generated by solar arrays at Target stores.

SunPower, a Silicon Valley solar panel manufacturer and power plant developer, will work with Ice Energy, a Colorado company that makes systems that use electricity when rates are low to form ice. When rates are high, air conditioning refrigerant is cooled by the melting ice rather than by an electricity-hogging compressor.

The Ice Bear system and a solar array will be installed at one Target store while battery packs will be used at two other stores in California.

The California Legislature has passed the nation’s first energy storage bill, which could result in the state’s utilities being required to bank a portion of the electricity they generate.

Assembly Bill 2514 now heads to the desk of Gov. Arnold Schwarzenegger, who has made climate change and green technology his political legacy as his final term winds down.

Energy storage is considered crucial for the mass deployment of wind farms, solar power plants, and other sources of intermittent renewable energy, as well to build out the smart grid.

On the West Coast, for instance, the wind tends to blow hardest at night when demand for electricity is low. If utilities can store that wind-generated power — and energy from solar farms — in batteries, flywheels, and other devices, they can avoid building and firing up those billion-dollar, greenhouse gas-emitting, fossil-fuel power plants that are only used when demand spikes.

AB 2514 won the support of Jerry Brown, the California attorney general who is the Democratic candidate for governor. The Sierra Club and union groups also support the measure. Various business organizations, including the California Chamber of Commerce, opposed the bill.

Originally, AB 2514 required California’s three big investor-owned utilities — PG&E, Southern California, and San Diego Gas & Electric — to have energy storage systems capable of providing at least 2.25 percent of average peak electrical demand by 2015. By 2020 the target would rise to at least 5 percent of average peak demand.

The bill now only requires that the California Public Utilities Commission determine the appropriate targets — if any — for energy storage systems, and then require the Big Three utilities to meet those mandates by 2015 and 2020. Publicly-owned utilities must set energy storage system targets to be met by 2016 and 2021.

Still, AB 2514 is a significant step and could ultimately help jump-start the market for energy storage, which remains in its infancy.

PG&E, for instance, plans to build an experimental facility that would tap electricity generated during peak wind farm production to pump compressed air into an underground reservoir. When demand jumps, the reservoir would release the air to run electricity-generating turbines which are capable of producing 300 megawatts of power.

And last week, PG&E proposed building a “pumped hydro” storage system. As its name implies, the system would pump water from one reservoir to another reservoir at a higher elevation during times of peak renewable energy production. Water in the upper reservoir would then be sent back downhill to power a turbine when electricity demand begins to spike.

photo: Todd Woody

This post first appeared on Grist.

The California Assembly has passed legislation that takes the first step to requiring that a percentage of electricity generated in the state be stored.

Electricity, of course, is the ultimate perishable commodity. If the bill is approved by the California Senate and signed by Gov. Arnold Schwarzenegger, it would apparently be the first time a state will move toward mandating that electricity generated by wind farms, solar power plants, and other intermittent sources be stored for use during peak demand.

That’s key if California is to meet its ambitious mandates to obtain 33 percent of its electricity from renewable sources by 2020.

“Electric energy storage is an emerging industry that offers the possibility to solve a number of major obstacles to the achievement of a sustainable electricity future,” according to an analysis of the legislation prepared by the California Public Utilities Commission in May. “It can effectively address problems such as the integration of intermittent renewables.”

Sponsored by Assembly member Nancy Skinner, a Berkeley Democrat, the bill has been watered down to make it palatable to the state’s utilities and regulators. It originally required the state’s utilities to obtain energy storage systems capable of providing at least 2.25 percent of average peak electrical demand by 2014. By 2020 the target would rise to at least 5 percent.

The latest version of the bill now wending its way through the state Senate requires the California Public Utilities Commission to open proceedings on energy storage and by October 2013 to adopt an initial target — if appropriate — for utilities to meet by the end of 2015.

California Attorney General Jerry Brown, the Democratic candidate for governor, is sponsoring the legislation, which is backed, not surprisingly, by the renewable energy industry and venture capitalists.

“It’s part of our bigger effort to deal with climate change,” Cliff Rechtschaffen, Special Assistant Attorney General, told me. “When we looked at how to develop renewables, the technology is here but stalled by lack of regulatory focus.”

Utilities spend billions of dollars building so-called peaker plants that operate just hours a year to supply electricity and avoid blackouts when demand spikes — say, on a hot day when everyone cranks up their air conditioners.

Such costs — and greenhouse gas emissions — could be cut or reduced if electricity stored from wind farms or solar power plants could be dispatched when demand rises.

A report prepared for the California Energy Commission and released this month concluded that adding gigawatts of wind and solar energy to the grid to meet renewable energy mandates would require “major alterations to system operations.”

Without storage, more natural gas power plants or hydroelectric facilities would need to be built to smooth out grid operations as increasing amounts of solar and wind energy comes online, according to the report prepared by Kema, an energy consulting firm.

“Storage can be up to two to three times as effective as adding a combustion turbine to the system,” the report stated.

The cost and feasibility of such storage systems is another matter, as it remains a nascent industry.

Most efforts focus on using batteries or mechanical systems like flywheels to store electricity. California utility PG&E has launched a pilot project to store electricity in the form of compressed air. Some developers of solar power plants intend to use molten salt to capture heat that can be released and used to drive an electricity-generating turbine after the soon goes down.

“This bill moves storage to the top of the regulatory agenda where it belongs,” says Rechtschaffe

Image: SolarReserve

Ok, I’m exaggerating a bit in the headline above but we’re getting closer to solar farms that will provide baseload power, operating at night and under cloudy conditions. As I write on Tuesday in The New York Times:

The holy grail of renewable energy is a solar power plant that continues producing electricity after the sun goes down.

A Santa Monica, Calif., company called SolarReserve has taken a step toward making that a reality, filing an application with California regulators to build a 150-megawatt solar farm that will store seven hours’ worth of the sun’s energy in the form of molten salt.

Heat from the salt can be released when it’s cloudy or at night to create steam that drives an electricity-generating turbine.

The Rice Solar Energy Project, to be built in the Sonoran Desert east of Palm Springs, will “generate steady and uninterrupted power during hours of peak electricity demand,” according to SolarReserve’s license application.

So-called dispatchable solar farms would in theory allow utilities to avoid spending billions of dollars building fossil fuel power plants that are fired up only a few times a year when electricity demand spikes, like on a hot day.

SolarReserve is literally run by rocket scientists, many of whom formerly worked at Rocketdyne, a subsidiary of the technology giant United Technologies. Rocketdyne developed the solar salt technology, which was proven viable at the 10-megawatt Solar Two demonstration project near Barstow, Calif., in the 1990s.

About Green Wombat

Green Wombat is written by
Todd Woody, a veteran environmental journalist based in California who writes for The New York Times, the Los Angeles Times, Grist and Yale e360. He's one of the few people on the planet who have held a northern hairy-nosed wombat in the wild.

Todd formerly was a senior editor at Fortune magazine, an assistant managing editor at Business 2.0 magazine and the business editor of the San Jose Mercury News.